One consequence of the two last world wars is that a large number of UXO's (unexploded ordnance) such as bombs, shells, grenades and mines still resides on the bottom or are buried in the bottom sediment. Deliberate dumping of chemical warfare weapons in the sea has also been performed during post war time. For example, it is estimated that more than 100.000 mines have been laid j in the Baltic Sea, of which approximately 30.000 have been disarmed so far. Hence still 70.000 mines are present which may cause severe damages during cable or pipeline installations or oil/gas production, etc.
Chemical weapons pose an environmental threat and can also be of great danger when caught in fishing nets. Thus, it is often necessary to perform accurate and high resolution surveying of the ocean bed, and the near region below the ocean bed, before any other underwater work or construction is done.
One commonly used method to search for UXO's or other objects with ferromagnetic signatures is to use one or several magnetometers that is either towed behind a survey vessel or mounted on a Remotely Operated Vehicle (ROV) which is operated from the survey vessel. Currently used methods use rather few magnetometers giving poor bottom coverage and ROVs when used are rather slow and have a limited lateral coverage. This makes surveying very time consuming and, since, survey vessels are expensive to operate there is a need for an improved system and method to decrease survey times.